Function igraph_blas_dgemv 

pub unsafe extern "C" fn igraph_blas_dgemv(
    transpose: igraph_bool_t,
    alpha: igraph_real_t,
    a: *const igraph_matrix_t,
    x: *const igraph_vector_t,
    beta: igraph_real_t,
    y: *mut igraph_vector_t,
) -> igraph_error_t